This invention relates to broadband communication systems and, more particularly, to improving the performance of terrestrial digital radio systems during periods of frequency-selective fading.
The reliability of terrestrial digital radio systems has been improved by the use of space-diversity and frequency-diversity techniques. When combined with so-called hitless (bit-by-bit) switching between on-line and standby radio receivers, these techniques reduce outage time caused by multipath fading phenomena.
On radio paths where outages are primarily due to frequency-selective (dispersive) multipath fading, it has been demonstrated that approaches based on pattern diversity provide protection equal to that of space diversity or frequency diversity but at lower cost. One known pattern-diversity approach requires two horizontally separated antennas which either are characterized by different beam patterns or are purposely misaligned in the elevation plane relative to boresight and to each other. While this approach does not need the expensive tall towers required by space-diversity systems, it still does require two separate antennas.
Another known pattern-diversity approach involves a single antenna with two separate main beams generated, for example, by using two purposely misaligned feeds. This approach provides protection against outage at the expense of deteriorated sidelobe performance and poor cross-polarization discrimination relative to that of a standard antenna.
Accordingly, efforts have continued by workers skilled in the art aimed at trying to devise other ways of improving the reliability of terrestrial digital radio systems during periods of frequency-selective fading. In particular, these efforts have concentrated on trying to develop a reliable system having a minimal amount of additional equipment and exhibiting good performance characteristics.